Illumination apparatus, hologram device, and vehicle control method

ABSTRACT

An illumination apparatus that illuminates an illumination zone having a first direction and a second direction crossing the first direction is provided with a light source to emit a coherent light beam, and a diffraction optical device to diffract the coherent light beam incident from the light source. The diffraction optical device diffracts the incident coherent light beam so that a width of the illumination zone in the second direction gradually becomes wider along the first direction of the illumination zone from a nearer side to the diffraction optical device.

TECHNICAL FIELD

The present disclosure relates to an illumination apparatus, a hologramdevice, and a vehicle control method, for illuminating an illuminationzone having a longitudinal direction and a lateral direction.

BACKGROUND ART

An illumination apparatus for illuminating a road surface with a desiredpattern in combination of a light source and a hologram device has beenproposed (see Patent Literature 1). In the illumination apparatusdisclosed in Patent Literature 1, a laser beam generated by a singlelight source is diffracted by a single hologram device.

PRIOR ART DOCUMENT Patent Literature

[Patent Literature 1] Japanese Patent Laid-Open No. 2015-132707

SUMMARY OF INVENTION

A laser beam has high coherency compared to a non-coherent light beamsuch as an LED light beam, and hence is capable of clearly illuminatinga desired zone in principle. However, in order to put the laser beam inpractical use in an illumination apparatus, it is required to devisevarious ways in apparatus configuration and projection pattern.

Although, by combining laser beams in a plurality of wavelength ranges,various colors can be formed, any technical ideas using laser beams in aplurality of wavelength ranges are not disclosed in Patent Literature 1.

Moreover, although, even in the case of using a laser beam in a singlewavelength range, an illumination form of an illumination zone can bechanged in various ways, any technical ideas for changing theillumination form of the illumination zone in various ways are notdisclosed in Patent Literature 1.

The present disclosure provides an illumination apparatus, a hologramdevice, and a vehicle control method, capable of optimizing theillumination form of the illumination zone even with a simpleconfiguration.

In order to solve the above problems, according to an aspect of thepresent disclosure, there is provided an illumination apparatus thatilluminates an illumination zone having a first direction and a seconddirection crossing the first direction comprising:

a light source to emit a coherent light beam; and

a diffraction optical device to diffract the coherent light beamincident from the light source,

wherein the diffraction optical device diffracts the incident coherentlight beam so that a width of the illumination zone in the seconddirection gradually becomes wider along the first direction of theillumination zone from a nearer side to the diffraction optical device.

A diffusion angle of the coherent light beam diffracted by thediffraction optical device in the second direction of the illuminationzone may be constant in an entire zone of the illumination zone in thefirst direction.

An illumination apparatus that illuminates an illumination zone having afirst direction and a second direction crossing the first directioncomprises:

a light source to emit a coherent light beam; and

a diffraction optical device to diffract the coherent light beamincident from the light source,

wherein the diffraction optical device may diffract the incidentcoherent light beam so that indicators are displayed in at least part ofthe illumination zone in the first direction.

The indicators may be displayed at a predetermined interval in the firstdirection of the illumination zone, and an illumination form of theindicators may be different from an illumination form of theillumination zone.

The indicators may be displayed at an end of the illumination zone inthe first direction, and an illumination form of the indicators may bedifferent from an illumination form of the illumination zone.

The indicators may be arranged so as to divide the illumination zone perpredetermined distance along the first direction.

The light source emits a plurality of coherent light beams in wavelengthranges different from one another,

wherein the diffraction optical device has:

a plurality of diffraction zones provided corresponding to the pluralityof coherent light beams, respectively, each diffraction zone diffractinga corresponding coherent light beam to illuminate the illumination zone;and

a synthesis optical system to combine the coherent light beamsdiffracted by the plurality of diffraction zones, respectively,

wherein the illumination zone may be illuminated with a coherent lightbeam combined by the synthesis optical system.

The light source emits a plurality of coherent light beams in wavelengthranges different from one another,

wherein the diffraction optical device has a diffraction plane, theplurality of coherent light beams being incident on the diffractionplane,

a plurality of element diffraction zones to diffract the plurality ofcoherent light beams, respectively, are arranged on the diffractionplane in a mixed manner, and

each of the plurality of element diffraction zones may illuminate theillumination zone.

According to another aspect of the present disclosure, an illuminationapparatus that illuminates an illumination zone having a first directionand a second direction crossing the first direction comprises:

a light source to emit a coherent light beam; and

a diffraction optical device to diffract the coherent light beamincident from the light source,

wherein the light source and the diffraction optical device may changean illumination form of the illumination zone.

The diffraction optical device has a plurality of diffraction zones, theplurality of diffraction zones illuminating partial zones that arearranged in the second direction in the illumination zone and differentfrom one another,

wherein the light source may vary a width of the illumination zone inthe second direction by switching as to whether to make the coherentlight beam incident on each of the plurality of diffraction zones.

The diffraction optical device has a plurality of diffraction zones, theplurality of diffraction zones illuminating partial zones that arearranged in the second direction in the illumination zone and differentfrom one another,

wherein the light source may vary a number to divide the illuminationzone in the second direction by switching as to whether to make thecoherent light beam incident on each of the plurality of diffractionzones.

The diffraction optical device has a plurality of diffraction zones toilluminate partial zones different from one another in the firstdirection in the illumination zone,

wherein the light source may vary an illumination length of theillumination zone in the first direction by switching as to whether tomake the coherent light beam incident on each of the plurality ofdiffraction zones.

The light source may change an illumination position on the illuminationzone in the first direction by switching an incidence angle of thecoherent light beam to the diffraction optical device.

An outgoing optical axis of the illumination apparatus may be switchedto change an illumination position on the illumination zone in the firstdirection.

The light source emits a plurality of coherent light beams in wavelengthranges different from one another,

wherein the diffraction optical device has a plurality of diffractionzones provided corresponding to the plurality of coherent light beams,respectively, each diffraction zone diffracting a corresponding coherentlight beam, and

the light source may change an illumination color of the illuminationzone by switching as to whether, on the plurality of diffraction zones,to make corresponding coherent light beams incident.

There is provided a detector to acquire environmental information onsurroundings of the illumination apparatus,

wherein the light source and the diffraction optical device may changean illumination form of the illumination zone based on the environmentalinformation acquired by the detector.

The illumination zone is a zone to illuminate part of a road closer to ashoulder of the road along a travel direction of a vehicle running onthe road,

wherein the detector detects whether a tire of the vehicle goes off to ashoulder side rather than to the illumination zone, and

the light source and the diffraction optical device may change anillumination form of the illumination zone when the detector detectsthat the tire of the vehicle goes off to the shoulder side rather thanto the illumination zone.

The illumination zone is a zone to illuminate part of a road along atravel direction of a vehicle running on the road,

wherein the detector detects an obstacle in front in a running directionof the vehicle, and

the light source and the diffraction optical device may change anillumination form of the illumination zone when the detector detects theobstacle.

The illumination zone is a zone to illuminate part of a road along atravel direction of a vehicle running on the road,

wherein the detector detects whether it is possible to pass through anarrow part in front in a running direction of the vehicle, and

the light source and the diffraction optical device may change anillumination form of the illumination zone in accordance with adetection result of the detector.

The illumination zone is a zone to illuminate part of a road along atravel direction of a vehicle running on the road,

wherein the detector detects at least one of speed and acceleration ofthe vehicle, and

the light source and the diffraction optical device may change anillumination target of the illumination zone based on at least one ofthe speed and acceleration of the vehicle detected by the detector.

The illumination zone is a zone to illuminate part of a road along atravel direction of a vehicle running on the road,

wherein the detector detects a slope in front in a running direction ofthe vehicle, and

the light source and the diffraction optical device may change anillumination form of the illumination zone in accordance with aninclination angle of the slope when the detector detects the slope.

According to an aspect of the present disclosure, there is provided ahologram device comprising a plural types of element hologram devicesfor diffracting coherent light beams in wavelength ranges different fromone another, the element hologram devices being provided by a pluralnumber for each type, the element hologram devices being arranged in afirst direction and a second direction crossing each other,

wherein two element hologram devices arranged next to each other in thefirst direction and the second direction diffract coherent light beamsin wavelength ranges different from each other.

The plural types of element hologram devices provided by the pluralnumber for each type may have a same number of element hologram devicesfor diffracting a coherent light beam in a wavelength range of red,element hologram devices for diffracting a coherent light beam in awavelength range of green, and element hologram devices for diffractinga coherent light beam in a wavelength range of blue.

According to an aspect of the present disclosure, there is provided ahologram device comprising a first element hologram device, a secondelement hologram device, and a third element hologram device arrangednext to one another in a first direction and a second direction crossingeach other,

wherein the first element hologram device diffracts a coherent lightbeam in a first wavelength range;

the second element hologram device diffracts a coherent light beam in asecond wavelength range, different from the coherent light beam in thefirst wavelength range; and

the third element hologram device diffracts a coherent light beam in athird wavelength range, different from the coherent light beams in thefirst wavelength range and in the second wavelength range.

According to an aspect of the present disclosure, there is provided avehicle control method comprising:

acquiring environmental information on surroundings of an illuminationapparatus;

making a coherent light beam incident from a light source to adiffraction optical device based on the acquired environmentalinformation;

the diffraction optical device performing diffraction in accordance withan incident coherent light beam to change an illumination form of anillumination zone; and

controlling a vehicle based on the acquired environmental information.

According to the present disclosure, the illumination form of theillumination zone can be optimized even with a simple configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically showing the configuration ofan illumination apparatus according to a first embodiment of the presentdisclosure;

FIG. 2 is a figure showing travel directions of coherent light beamsdiffracted by a plurality of hologram devices;

FIG. 3 is a plan view of an illumination zone viewed from a normaldirection;

FIG. 4 is a figure explaining an adjustment method of diffractioncharacteristics of a plurality of hologram devices placed vertically;

FIG. 5 is a figure showing a positional relationship between eachhologram device and an illumination zone viewed from a normal directionof the illumination zone;

FIG. 6 is a figure showing an example in which each hologram deviceincludes a plurality of element hologram devices;

FIG. 7 is a perspective view showing an example in which a plurality ofhologram devices are arranged in a lateral direction of an illuminationzone;

FIG. 8 is a schematic plan view of FIG. 7 viewed from above;

FIG. 9 is a figure explaining an adjustment method of diffractioncharacteristics of two hologram devices adjacent to each other along alateral direction of an illumination zone;

FIG. 10 is a figure showing a trapezoidal illumination zone visuallyperceived by human eyes;

FIG. 11 is a figure showing an illumination range of an illuminationzone;

FIG. 12 is a figure showing a rectangular illumination zone visuallyperceived by human eyes;

FIG. 13 is a perspective view schematically showing the configuration ofan illumination apparatus provided with an optical scanning device;

FIG. 14 is a figure showing an illumination zone according to a secondembodiment;

FIG. 15 is a plan view of the illumination zone of FIG. 14 viewed from anormal direction;

FIG. 16A shows an example of an illumination zone to be illuminated by afirst element hologram device or a first hologram device;

FIG. 16B shows an example of indicators to be illuminated by a secondelement hologram device or a second hologram device;

FIG. 17 is a figure showing an illumination zone according to a thirdembodiment;

FIG. 18 is a plan view of the illumination zone of FIG. 17 viewed from anormal direction;

FIG. 19 is a figure showing an illumination zone according to a fourthembodiment;

FIG. 20 is a plan view of the illumination zone 4 of FIG. 19 viewed froma normal direction;

FIG. 21 is a figure schematically showing the optical configuration ofdiffraction optical devices and their surroundings according to a fifthembodiment;

FIG. 22 is a figure showing one modification example of a method ofpreventing the occurrence of color shift, different from the method inFIG. 21;

FIG. 23 is a figure showing an example of varying the width of aline-like illumination zone in a lateral direction;

FIG. 24 is a figure showing an example of varying the width orillumination position of a line-like illumination zone in a longitudinaldirection;

FIG. 25 is a figure explaining one modification example of FIG. 24;

FIG. 26A is a figure schematically showing an example of changing anoutgoing optical-axis direction of an illumination apparatus having alight source and a hologram device;

FIG. 26B is a figure schematically showing an example of changing anoutgoing optical-axis direction of an illumination apparatus having alight source and a hologram device;

FIG. 27 is a perspective view schematically showing the configuration ofan illumination apparatus according to a ninth embodiment of the presentdiscloser; and

FIG. 28 is a perspective view schematically showing the configuration ofan illumination apparatus according to a twelfth embodiment of thepresent discloser.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, an embodiment of the present disclosure will be explainedwith reference to the drawings. In the accompanying drawings of thepresent specification, for simplicity in drawings and easyunderstanding, the scale, the ratio of height to width, etc. aremodified to be exaggerated from those of actual ones, according to need.

The terms such as “parallel”, “intersect”, and “the same”, and thevalues of, for example, length and angle, which define shape,geometrical condition, and the degree of shape and geometricalcondition, used in the present specification, are not necessary belimited to their strict definitions, but are interpreted to include therange to the extent that a similar function can be expected.

First Embodiment

FIG. 1 is a perspective view schematically showing the configuration ofan illumination apparatus 1 according to a first embodiment of thepresent disclosure. The illumination apparatus 1 of FIG. 1 is used, forexample, as a portion of a headlight of a vehicle. However, theillumination apparatus 1 of FIG. 1 is applicable as a variety ofillumination lights such as a tail light of the vehicle and asearchlight. The vehicle includes, not only a vehicle such as anautomobile, but also a variety of the vehicle, such as a ship and anairplane, provided with the illumination apparatus 1. Hereinbelow, anexample in which the illumination apparatus 1 of FIG. 1 is applied to aportion of a headlight of a vehicle, will be explained.

The illumination apparatus 1 of FIG. 1 is provided with light sources 2and a plurality of diffraction optical devices 3. The light sources 2emit a coherent light beam such as a laser beam. In the example of FIG.1, although a plurality of light sources 2 are provided by the samenumber as the plurality of diffraction optical devices 3, the number ofthe light sources 2 is any number. Hereinbelow, an example in which onelight source 2 is provided for each diffraction optical device 3, willbe explained. The light source 2 is typically a laser light source 2that emits a laser beam. Although there are a variety of types for thelaser light source 2 such as a semiconductor laser, any type of thelaser light source 2 is applicable.

The illumination apparatus 1 according to the first embodiment is notalways necessary to be provided with a plurality of light sources 2 anda plurality of diffraction optical devices 3. It is enough for theillumination apparatus 1 to be provided with one light source 2 and onediffraction optical device 3. However, hereinbelow, an example of theillumination apparatus 1 provided with a plurality of light sources 2and a plurality of diffraction optical devices 3, will be explained.

The wavelength ranges of coherent light beams to be emitted by theplurality of light sources 2 may be the same as or different from oneanother. However, hereinbelow, an example in which the plurality oflight sources 2 emit coherent light beams in wavelength ranges differentfrom one another, will be explained. Coherent light beams in wavelengthranges different from one another are, for example, coherent light beamsin wavelength ranges of red, green and blue, three in total. It is amatter of course that the light sources 2 may emit coherent light beamsof colors other than red, green and blue. Moreover, a plurality of lightsources 2 in the same wavelength range may be provided to improveillumination intensity on an illumination zone 4.

The plurality of diffraction optical devices 3 diffract coherent lightbeams incident from the light sources 2, respectively, to illuminate theentire zone of the illumination zone 4. The illumination zone has afirst direction and a second direction crossing each other. For example,a longitudinal direction and a lateral direction which will be describedlater may be the first direction and the second direction, respectively.In more specifically, each of the plurality of diffraction opticaldevices 3 diffracts an incident coherent light beam so that the width ofthe illumination zone 4 in the lateral direction gradually becomes wideralong the longitudinal direction of the illumination zone 4 from anearer side to the diffraction optical device 3.

The plurality of diffraction optical devices 3 are typically a pluralityof hologram devices 3. As described later, by using the hologram devices3 as the diffraction optical devices 3, it becomes easier to design thediffraction characteristics of each hologram device 3 and alsorelatively easy to design illumination such that each hologram device 3illuminates the entire zone of the illumination zone 4. Hereinbelow, anexample in which, as the plurality of diffraction optical devices 3, aplurality of hologram devices 3 are used, will be explained.

The illumination apparatus 1 of FIG. 1 is provided with a plurality ofshaping optical systems 5 arranged between the plurality of lightsources 2 and the plurality of hologram devices 3. Each shaping opticalsystem 5 shapes a coherent light beam emitted from the correspondinglight source 2 and converts the coherent light beam into a parallelbeam.

In more specifically, each shaping optical system 5 has a first lens 6to widen the beam diameter of a coherent light beam emitted from thelight source 2 and a second lens 7 to convert the coherent light beamthat has passed through the first lens 6 into a parallel beam. Thecoherent light beam converted into the parallel beam by the second lens7 is incident on the corresponding hologram device 3. The opticalconfiguration of the shaping optical system 5 is not limited to that ofFIG. 1.

To each hologram device 3, a coherent light beam that has been emittedby the corresponding light source 2 and then shaped by the correspondingshaping optical system 5 is incident. Each hologram device 3 diffractsthe incident coherent light beam to illuminate the entire zone of theillumination zone 4.

The illumination zone 4 is provided on a predetermined two-dimensionalplane in an angle space in which light beams diffracted by the pluralityof hologram devices 3 travel. The illumination zone 4 according to thepresent embodiment has a longitudinal direction dl and a lateraldirection dw. In more specifically, the illumination zone 4 is aline-like illumination range having a predetermined width in the lateraldirection dw and extending in the longitudinal direction dl. The widthin the lateral direction dw is finite, however, it does not matter aboutthe length in the longitudinal direction dl. Moreover, it is not alwaysnecessary to provide one illumination zone 4. When, for example, theillumination apparatus 1 according to the present embodiment is built inthe vehicle, two line-like illumination zones 4 having the longitudinaldirection dl in front and rear directions of the vehicle may be arrangedwith a gap therebetween, the gap being equal to the width of thevehicle. An advantage of the arrangement of two line-like illuminationzones 4 with the gap equal to the width of the vehicle is that, whenthere is an obstacle in the vehicle travel direction, it can be easilydetermined by means of the gap between the two line-like illuminationzones 4 whether it is possible to avoid the obstacle to travel.

The plurality of hologram devices 3 in FIG. 1 are placed verticallyalong a normal direction nd of the illumination zone 4. In other words,the plurality of hologram devices 3 are placed vertically along thenormal direction nd of the illumination zone 4 that is disposed on apredetermined two-dimensional plane in an angle space in which a lightbeam diffracted by each hologram device 3 travels.

FIG. 2 is a figure showing travel directions of coherent light beamsdiffracted by the plurality of hologram devices 3. As described above,each hologram device 3 of FIG. 2 illuminates the entire zone of theillumination zone 4.

However, as shown in FIG. 2, when the plurality of hologram devices 3are placed vertically, the illumination ranges of diffracted light beamsof the hologram devices 3 do not always meet one another. As shown inFIG. 3, the illumination ranges may be displaced in both of the lateraldirection dw and the longitudinal direction dl of the illumination zone4. FIG. 3 shows an example of displacement in which a solid-lineillumination range 4 a is the correct illumination zone 4 whereas abroken line indicates a displaced illumination range 4 b.

It is therefore, as shown in FIG. 2, when the plurality of hologramdevices 3 are placed vertically, it is necessary to adjust diffractioncharacteristics per hologram device 3 so that the illumination rangemeets the illumination zone 4. In more specifically, it is required forrespective hologram devices 3 to adjust the diffraction characteristicsso that the positions of both edges that pass through both ends of theillumination zone 4 in the lateral direction dw to extend in thelongitudinal direction dl meet one another, and the positions of bothedges that pass through both ends of the illumination zone 4 in thelongitudinal direction dl to extend in the lateral direction dw meet oneanother.

As described later, when each hologram device 3 has a plurality ofelement hologram devices 3 c each illuminating the entire zone of theillumination zone 4, it is required for the respective element hologramdevices 3 c to adjust the diffraction characteristics so that thepositions of four edges in total that extend in the longitudinaldirection dl and the lateral direction dw meet one another.

FIG. 4 is a figure explaining an adjustment method of the diffractioncharacteristics of the plurality of hologram devices 3 placedvertically. FIG. 4 shows an example in which a first hologram device 3 ais disposed upward by a distance b from a two-dimensional plane in whichthe illumination zone 4 is present and a second hologram device 3 b isdisposed upward by a distance a from the first hologram device 3 a. FIG.4 shows an example in which illumination ranges meet each other at aposition r apart from the first hologram device 3 a and the secondhologram device 3 b by a distance R in the longitudinal direction dl ofthe illumination zone 4. An angle between the direction of a light beamdirected toward the position r from the first hologram devices 3 a andthe two-dimensional plane in which the illumination zone 4 is present isdenoted as θ1, and an angle between the direction of a light beamdirected toward the position r from the second hologram devices 3 b andthe two-dimensional plane is denoted as θ2.

The following expression (1) holds among the angle θ1, the distance b,and the distance R.tan θ1=b/R  (1)

Moreover, the following expression (2) holds among the angle θ2, thedistance a, the distance b, and the distance R.tan θ2=(b+a)/R  (2)

By adjusting the diffraction characteristics of respective hologramdevices 3 for each distance R so as to satisfy the above expressions (1)and (2), the positions of both edges that pass through the both ends ofthe illumination zone 4 in the longitudinal direction dl to extend inthe lateral direction dw can meet one another.

In order to align the positions of both edges that pass through bothends of the illumination zone 4 in the lateral direction dw to extend inthe longitudinal direction dl to meet one another, the diffractioncharacteristics of each hologram device 3 may be adjusted based on FIG.5. FIG. 5 is a figure showing a positional relationship between eachhologram device 3 and the illumination zone 4 viewed from the normaldirection of the illumination zone 4. Since the hologram devices 3 areplaced vertically in the normal direction of the illumination zone 4,FIG. 5 shows only one hologram device 3. In FIG. 5, the angle range of adiffracted light beam of the hologram device 3 is θ1 ⁺+θ1 ⁻, R being theshortest distance from the position of the hologram device 3 to anarbitrary position in the illumination zone 4.

The angles θ1 ⁺, θ1 ⁻ in FIG. 5 are expressed by the followingexpressions (3) and (4), respectively.tan θ1⁺ =L/(2R)  (3)tan θ1⁻ =−L/(2R)  (4)

A condition for illumination with a width equal to the width of theillumination zone 4 in the lateral direction dw at a position with thedistance R from the hologram device 3 is that the hologram device 3 hasdiffraction angles θ1 ⁺ and θ1 ⁻ that satisfy the expressions (3) and(4), respectively. As understood from the expressions (3) and (4), evenif a width L of the illumination zone 4 in the lateral direction dw isconstant, when the distance R varies, the angles θ1 ⁺ and θ1 ⁻ vary. Inother words, the adjustment of diffraction characteristics of eachhologram device 3 is required to be performed for each distance R. Asdescribed above, by adjusting the diffraction characteristics ofrespective hologram devices 3 so as to satisfy the above expressions (3)and (4), the positions of both edges that pass through both ends of theillumination zone 4 in the lateral direction dw to extend in thelongitudinal direction dl can meet one another.

In summarizing the above, when the plurality of hologram devices 3 areplaced vertically, by adjusting the diffraction characteristics of eachhologram device 3 based on the above-described expressions (1) to (4),the ranges illuminated by the hologram devices 3 can meet one another.Accordingly, blurring on the border of the illumination zone 4 can bereduced to enable human eyes to visually perceive the illumination zone4 clearly.

As described above, in order to match the positions of both ends of theillumination zone 4 in the longitudinal direction dl and also both endsin the lateral direction dw to meet one another for the plurality ofhologram devices 3, it is required to adjust the diffractioncharacteristics of the hologram devices 3 for each distance R describedabove, based on the expressions (1) to (4).

In the present embodiment, in order to perform such an adjustment oncomputer, it is presupposed to use a computer generated hologram (CGH)as the plurality of hologram devices 3. Since the CGH does not require alight source 2 for emitting object light, an optical system for formingan interference fringe, and a blank hologram recording medium forforming an interference fringe, and an interference-fringe recordingprocess can be performed on computer, and thus it is easy to generate aninterference fringe having any diffraction characteristics.

Each of the plurality of hologram devices 3 in FIG. 1 may have aplurality of element hologram devices 3 c divided vertically andhorizontally. Each element hologram device 3 c has diffractioncharacteristics capable of illuminating the entire zone of theillumination zone 4. The element hologram devices 3 c may not have thesame size. Among the plurality of hologram devices 3, a part of thehologram devices 3 may only have a plurality of element hologramswhereas the remaining hologram devices 3 may have a unitaryconfiguration. However, hereinbelow, for easy explanation, an example ofthe hologram devices 3 each having the plurality of element hologramdevices 3 c, will be explained.

Each hologram device 3 has the plurality of element hologram devices 3 cand each element hologram device 3 c illuminates the entire zone of theillumination zone 4, so that the safety of a laser beam (coherent lightbeam) can be improved with weakened laser brightness when the hologramdevice 3 is observed from the illumination zone 4's side. Since eachelement hologram device 3 c diffuses a coherent light beam incident onan incidence surface thereof toward the entire zone of the illuminationzone 4, the brightness of the hologram device 3 when observed from theillumination zone 4's side is much weaker than the brightness of acoherent light beam emitted from the light source 2. Therefore, evenline of light is directed toward the direction of the light source 2from any point in the illumination zone 4, the possibility of hurtinghuman eyes is reduced. Moreover, on respective points in theillumination zone 4, coherent light beams from the plurality of elementhologram devices 3 c are incident at incidence angles different from oneanother. Accordingly, light interference patterns are overlapped oneanother with no correlation to be averaged, and, as a result, in theillumination zone 4, speckles to be observed by human eyes becomeinconspicuous.

Although FIG. 1 shows the example of the plurality of hologram devices 3placed vertically in the normal direction of the illumination zone 4, asshown in FIG. 7, the plurality of hologram devices 3 may be arranged inthe lateral direction dw of the illumination zone 4.

FIG. 8 is a schematic plan view of FIG. 7 viewed from above. Forsimplification, FIG. 8 shows two from among the three light sources 2,two from among the three shaping optical systems 5, and two from amongthe three hologram devices 3, provided in FIG. 7.

When the plurality of hologram devices 3 are arranged in the lateraldirection dw of the illumination zone 4, if the hologram devices 3 havethe same diffraction characteristics, illumination ranges of diffractedlight beams of the hologram devices 3 are displaced from one another asshown in FIG. 8. This displacement occurs on both edges that passthrough both ends of the illumination zone 4 in the lateral direction dwto extend in the longitudinal direction dl. Therefore, both edges of theillumination zone 4 may blur.

It is therefore desirable to adjust the diffraction characteristics ofthe plurality of hologram devices 3 one by one so that the illuminationranges of diffracted light beams of the hologram devices 3 overlap oneanother as much as possible. In other words, it is desirable to adjustthe diffraction characteristics of the hologram devices 3 so that thepositions of both edges that pass through both ends of the illuminationzone 4 in the lateral direction dw to extend in the longitudinaldirection dl meet one another among the hologram devices 3.

FIG. 9 is a figure explaining an adjustment method of the diffractioncharacteristics of two hologram devices 3 (hereinbelow, a first hologramdevice 3 a and a second hologram device 3 b) adjacent to each otheralong the lateral direction dw of the illumination zone 4. FIG. 9 showsan example in which, the illumination zone 4 has a width L in thelateral direction dw, the first hologram device 3 a is disposed on aline that passes through the center of the illumination zone 4 in thelateral direction dw to extend in the longitudinal direction dl, and thesecond hologram device 3 b is disposed apart from the first hologramdevices 3 a by the distance a in the lateral direction dw of theillumination zone 4.

In FIG. 9, it is defined that a diffracted light beam of the firsthologram device 3 a has an angle range of θ1 ⁺+θ1 ⁻, and a diffractedlight beam of the second hologram device 3 b has an angle range of θ2⁺+θ2 ⁻, R being the shortest distance from the positions of the firsthologram device 3 a and the second hologram device 3 b to an arbitraryposition in the illumination zone 4.

Angles θ1 ⁺ and θ1 ⁻ in FIG. 9 are expressed by the followingexpressions (5) and (6), respectively.tan θ1⁺ =L/(2R)  (5)tan θ1⁻ =−L/(2R)  (6)

Moreover, angles θ2 ⁺ and θ2 ⁻ in FIG. 9 are expressed by the followingexpressions (7) and (8), respectively.tan θ2⁺=1/R×(L/2−a)  (7)tan θ2⁻=1/R×(−L/2−a)  (8)

As described above, a condition for illumination with a width equal tothe width of the illumination zone 4 in the lateral direction dw at aposition with the distance R from the first hologram device 3 a is thatthe first hologram device 3 a has diffraction angles θ1 ⁺ and θ1 ⁻ thatsatisfy the expressions (5) and (6), respectively. Likewise, a conditionfor illumination with a width equal to the width of the illuminationzone 4 in the lateral direction dw at a position with the distance Rfrom the second hologram device 3 b is that the second hologram device 3b has diffraction angles θ2 ⁺ and θ2 ⁻ that satisfy the expressions (7)and (8), respectively.

As understood from the expressions (5) to (8), even if the width L ofthe illumination zone 4 in the lateral direction dw is constant, whenthe distance R varies, the angles θ1 ⁺, θ1 ⁻, θ2 ⁺, and θ2 ⁻ vary. Inother words, the adjustments of diffraction characteristics of the firsthologram device 3 a and the second hologram device 3 b are required tobe performed for each distance R.

As described above, in order to match the positions of both edges of theillumination zone 4 in the longitudinal direction dl to meet one anotheramong the plurality of hologram devices 3, it is required to adjust thediffraction characteristics of the hologram devices 3 for each distanceR described above, based on the expressions (5) to (8).

(Unique Configuration of First Embodiment)

FIG. 5 described above shows an example in which the width of theillumination zone 4 in the lateral direction dw is constant at any pointof the illumination zone 4 in the longitudinal direction dl. In thiscase, as shown in FIG. 10, the illumination zone 4 is visually perceivedas having a larger width in the lateral direction at a nearer side ofthe illumination zone 4 to human eyes whereas having a smaller width inthe lateral direction at a farther side of the illumination zone 4 fromthe human eyes. According to the inspection by the present inventor, itis found that although the illumination zone 4 is visually perceived ashaving a smaller width in the lateral direction at the farther side ofthe illumination zone 4, since a coherent light beam is used as thelight source 2, the illumination zone 4 can be visually perceivedclearly up to the farther side of the illumination zone 4.

It is known that the optical output of the light source 2 that emits acoherent light beam depends on the product of the illuminance and thearea of illumination of the illumination zone 4. When the illuminance ofthe illumination zone 4 is not varied, the light source 2 requiressmaller optical output for a smaller area of illumination. Therefore, inthe present embodiment, the length of a line-like illumination zone 4 inthe lateral direction is set at the farthest end of the illuminationzone 4 in the longitudinal direction so that, when a human present inthe vicinity of the hologram devices 3 looks out the illumination zone 4over the farthest direction in the longitudinal direction, the human canvisually perceive correctly the farthest end of the illumination zone 4in the longitudinal direction. In more specifically, the length of theillumination zone 4 in the lateral direction is varied to a pluralnumber of lengths at the farthest end of the illumination zone 4 in thelongitudinal direction, and the length of the illumination zone 4 in thelateral direction at the farthest end of the illumination zone 4 in thelongitudinal direction is set in accordance with the shortest lengththat can be visually perceived by the human.

Next, a diffusion angle of each hologram device 3 is set so that thelength of the illumination zone 4 in the lateral direction at thefarthest end of the illumination zone 4 in the longitudinal direction isset to the above-described set value and the length of the illuminationzone 4 in the lateral direction can be visually perceived as beingconstant over the entire zone of the illumination zone 4 in thelongitudinal direction. In this setting, the diffusion angle of eachhologram device 3 is set to be always constant irrespective of theposition on the illumination zone 4 in the longitudinal direction.Accordingly, the illumination range of the illumination zone 4 viewedfrom the normal direction nd becomes a trapezoid as shown in FIG. 11from a rectangle such as in FIG. 5. In more specifically, theillumination range of the illumination zone 4 becomes a trapezoid thathas the shortest length in the lateral direction at one end of theillumination zone 4 in the longitudinal direction closer to eachhologram device 3 and the longest length in the lateral direction atanother end of the illumination zone 4 in the longitudinal directionfarthest from each hologram device 3.

Accordingly, the area of the trapezoidal illumination range in FIG. 11can be reduced as understood by comparison with the rectangularillumination range shown by a broken line. In other words, this meansthat the optical output of the light source 2 that emits a coherentlight beam can be reduced.

As described above, when the illumination range of the illumination zone4 is formed into a trapezoid as shown in FIG. 11, an effect is given insuch a manner that the width of the illumination zone 4 in the lateraldirection can be visually perceived by human eyes as being almostconstant at any position on the illumination zone 4 in the longitudinaldirection, as shown in FIG. 12. As a matter of course, an apparentlength of the illumination zone 4 in the lateral direction variesdepending on the height of human eyes and the distance between theillumination zone 4 and the position of the human eyes. Therefore, thewidth of the illumination zone 4 in the lateral direction may not alwaysbe constant at any position in the longitudinal direction. However, thedifference in width of the illumination zone 4 in the lateral directionis visually perceived as being smaller.

In this case, the diffusion angle of each hologram device 3 is alwaysconstant irrespective of the position on the illumination zone 4 in thelongitudinal direction. Such a setting of the diffusion angle of eachhologram device 3 can be performed comparatively easily when the CGH isused as the hologram device 3.

An example explained in FIG. 1 provides a plurality of light sources 2that emit a plurality of coherent light beams in wavelength rangesdifferent from one another and a plurality of hologram devices 3.However, only one light source 2 and also only one hologram device 3 maybe provided. In the case of only one light source 2 and only onehologram device 3, although the illumination color of the illuminationzone 4 is a single color, by forming the illumination range of theillumination zone 4 into a trapezoid in the same manner as in FIG. 11,the width of the illumination zone 4 in the lateral direction can beapparently constant.

Moreover, when the hologram device 3 is divided into a plurality ofelement hologram devices 3 c, a part of the element hologram devices 3 cmay illuminate the illumination zone 4 in a rectangular shape as shownin FIG. 5, and at least another part of the element hologram devices 3 cmay illuminate the illumination zone 4 in a trapezoidal shape as shownin FIG. 10. By means of a beam scanning device 8 shown in FIG. 13, theelement hologram devices 3 c on which a coherent light beam from thelight source 2 is to be incident can be switched to select whether theillumination form of the illumination zone 4 visually perceived by ahuman is set as shown in FIG. 10 or FIG. 12.

As described above, in the first embodiment, under the condition thatthe farthest end of the illumination zone 4 in the longitudinaldirection can be visually perceived by human eyes, the width of theillumination zone 4 in the lateral direction is made to be visuallyperceived by the human eyes as being almost the same width over theentire zone of the illumination zone 4 in the longitudinal direction. Inthis way, although the illumination zone 4 becomes a trapezoid, it isvisually perceived as a rectangle by the human eyes. By forming theillumination zone 4 into a trapezoid, the area of the illumination zone4 can be reduced further to reduce the optical output of the lightsource 2. Therefore, the light source 2 can be made compact with areduced parts cost, and heat generation from the light source 2 can berestricted to improve durability of the light source 2. Moreover, sincethe width of the illumination zone 4 in the lateral direction can bevisually perceived by the human eyes as being constant over the entirezone of the illumination zone 4 in the longitudinal direction, visualperception of the illumination zone 4 is improved. Furthermore, theillumination zone 4 can be illuminated by setting the diffusion angle ofeach hologram device 3 to a constant angle irrespective of the positionon the illumination zone 4 in the longitudinal direction. Therefore, thediffraction characteristics of each hologram device 3 can be setrelatively easily.

Second Embodiment

A second embodiment displays an indicator in the illumination zone 4.

An illumination apparatus 1 according to the second embodiment has thesame configuration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment.

The illumination apparatus 1 according to the second embodimentilluminates a line-like illumination zone 4, in the same manner as thefirst embodiment. The first embodiment shows an example in which thewidth of the illumination zone 4 in the lateral direction can bevisually perceive by human eyes as being constant over the entire zoneof the illumination zone 4 in the longitudinal direction. The secondembodiment may be the same as the first embodiment or may be configuredin such a manner that the width of the illumination zone 4 in thelateral direction is visually perceived by human eyes in a manner thatthe width in the lateral direction becomes smaller at a farther side inthe longitudinal direction.

FIG. 14 is a figure showing an illumination zone 4 according to thesecond embodiment, showing the state of the illumination zone 4 visuallyperceived by human eyes. An example shown here is that an actualillumination range of the illumination zone 4 is a rectangle as shown inFIG. 5, and the width of the illumination zone 4 in the lateraldirection is visually perceived by the human eyes in such a manner thatthe width in the lateral direction becomes smaller at a farther side inthe longitudinal direction. FIG. 15 is a plan view of the illuminationzone 4 of FIG. 14 viewed from the normal direction.

In the illumination zone 4 according to the present embodiment,indicators 9, for example, formed with lateral lines are displayed perpredetermined distance. It is desirable that the predetermined distancehas a value of, for example, 10 meters or 100 meters by which anaccumulated distance can be easily known. A display color of theindicators 9 is desirably a color distinguishable from the display colorof the illumination zone 4. In the case of an illumination apparatus 1provided with one light source 2 and one hologram devices 3, theindicators 9 may be displayed with a broken line or a thick line so asto be distinguishable from the illumination zone 4. As described above,the illumination form of the indicators 9 is different from lineillumination of the illumination zone 4. The difference in illuminationform may be the difference in color, line width, line type, shape, etc.

By displaying the indicators 9 such as shown in FIG. 14, as beingsuperposed on the illumination zone 4, it is easy to know the distanceof the illumination zone 4 in the longitudinal direction. For example,when the indicators 9 are displayed at a 10-meter interval, it is easyto recognize that the distance from the forefront to the rearward thirdindicator 9 is 3×10=30 meters.

The indicators 9 according to the second embodiment can be easilydisplayed by adjusting the diffusion characteristics of a part ofelement hologram devices 3 c of one or a plurality of hologram devices3. For example, when displaying the indicators 9 in a color differentfrom the illumination color of the illumination zone 4, it may beconfigured such that diffracted light beams from hologram devices 3different from one another are incident on the display positions of theindicators 9 and the other illumination positions of the illuminationzone 4. Or hologram devices 3 that are not shown may be provided, otherthan the hologram devices 3 for line illumination, to illuminate theindicators 9.

Or, when each of the plurality of hologram devices 3 has a plurality ofelement hologram devices 3 c, element hologram devices 3 c fordisplaying the indicators 9 may be provided other than the elementhologram devices 3 c for illuminating the illumination zone 4.

FIG. 16A shows an example of the illumination zone 4 to be illuminatedby a first element hologram device or a first hologram device. FIG. 16Bshows an example of the indicators 9 to be illuminated by a secondelement hologram device or a second hologram device. By superposing theillumination zone 4 of FIG. 16A and the indicators 9 of FIG. 16B, theindicators 9 are displayed as being superposed on the illumination zone4 as shown in FIGS. 14 and 15.

In the above-described example, the indicators 9 are displayed at apredetermined interval in the illumination zone 4. However, the intervalof the indicators 9 may not necessary be uniform. For example, in thecase of the illumination apparatus 1 for use in a headlamp of vehicle,the interval of the indicators 9 may be smaller as the indicators 9 arecloser to the vehicle whereas larger as the indicators 9 are fartherfrom the vehicle.

As described, in the second embodiment, since the indicators 9 aredisplayed as being superposed on the line-like illumination zone 4 at apredetermined interval, the length of the illumination zone 4 in thelongitudinal direction can be easily recognized. Therefore, byilluminating the line-like illumination zone 4 along a vehicle traveldirection and by displaying the indicators 9 as being superposed on theillumination zone 4, it is easier to sharpen the sense of distance inthe vehicle travel direction, so that, for example, the distance to anobstacle or a target can be correctly recognized.

Third Embodiment

A third embodiment displays indicators on both ends of a line-likeillumination zone 4 in the longitudinal direction.

An illumination apparatus 1 according to the third embodiment has thesame configuration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment.

The illumination apparatus 1 according to the third embodimentilluminates a line-like illumination zone 4, in the same manner as thefirst embodiment. The first embodiment shows an example in which thewidth of the illumination zone 4 in the lateral direction dw can bevisually perceived by human eyes as being constant over the entire zoneof the illumination zone 4 in the longitudinal direction dl. The thirdembodiment may be the same as the first embodiment or may be configuredin such a manner that the width of the illumination zone 4 in thelateral direction dw is visually perceived by the human eyes in a mannerthat the width in the lateral direction dw becomes smaller at a fartherside in the longitudinal direction dl.

FIG. 17 is a figure showing an illumination zone 4 according to thethird embodiment, showing the state of the illumination zone 4 visuallyperceived by human eyes. An example shown here is that an actualillumination range of the illumination zone 4 is a rectangle as shown inFIG. 5, and the width of the illumination zone 4 in the lateraldirection dw is visually perceived the human eyes in such a manner thatthe width in the lateral direction dw becomes smaller at a farther sidein the longitudinal direction dl. FIG. 18 is a plan view of theillumination zone 4 of FIG. 17 viewed from the normal direction.

As shown in FIGS. 17 and 18, indicators 9 are displayed on both ends ofa line-like illumination zone 4 in the longitudinal direction dl. Theillumination form of the indicators 9 is different from lineillumination of the illumination zone 4. In more specifically, theindicators 9 are different from line illumination in at least one ofcolor, line width, line type, and shape. For example, with lineillumination in white, the indicators 9 may be illuminated with a color,such as red, distinguishable from white.

By displaying the indicators 9 on both ends of the illumination zone 4in the longitudinal direction dl, it is easier to know a start point andan end point of the illumination zone 4. For example, when the length ofthe illumination zone 4 in the longitudinal direction dl ispredetermined, it is easier to know the end point of the illuminationzone 4.

The indicators 9 of the third embodiment can be displayed on both endsof the illumination zone 4 in the longitudinal direction dl by the samemethod as for the indicators 9 of the second embodiment, using at leasta part of the hologram devices 3. For example, by using element hologramdevices 3 c different from element hologram devices 3 c for lineillumination, illumination may be performed on both ends of theillumination zone 4 in the longitudinal direction dl in a differentillumination form. Or hologram devices 3, other than the plurality ofhologram devices 3 for line illumination, may be provided to illuminatethe indicators 9.

As described above, in the third embodiment, since the indicators 9 aredisplayed on both ends of the line-like illumination zone 4 in thelongitudinal direction dl, it is easier to know the start point and theend point of the illumination zone 4. Therefore, even if the length ofthe illumination zone 4 in the longitudinal direction dl is very long,it is easier to know the farthest end position of the illumination zone4.

Other than displaying the indicators on both ends as described above,the indicators may be displayed only on one end. Specifically, theindicators may be displayed only on an end closer to the light source,that is, only at the start point of the illumination zone, or only on anend farthest from the light source, that is, at the end point of theillumination zone 4.

Fourth Embodiment

A fourth embodiment provides indicators 9 that divide the illuminationzone 4 along the longitudinal direction dl per predetermined distance.

An illumination apparatus 1 of the fourth embodiment has the sameconfiguration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment.

The illumination apparatus 1 according to the fourth embodimentilluminates a line-like illumination zone 4, in the same manner as thefirst embodiment. The first embodiment shows an example in which thewidth of the illumination zone 4 in the lateral direction dw can bevisually perceived by human eyes as being constant over the entire zoneof the illumination zone 4 in the longitudinal direction dl. The fourthembodiment may be the same as the first embodiment or may be configuredin such a manner that the width of the illumination zone 4 in thelateral direction dw is visually perceived by the human eyes in a mannerthat the width in the lateral direction becomes smaller at a fartherside in the longitudinal direction.

FIG. 19 is a figure showing an illumination zone 4 according to thefourth embodiment, showing the state of the illumination zone 4 visuallyperceived by human eyes. An example shown here is that an actualillumination range of the illumination zone 4 is a rectangle as shown inFIG. 5, and the width of the illumination zone 4 in the lateraldirection dw is visually perceived in such a manner that the width inthe lateral direction dw becomes smaller at a farther side in thelongitudinal direction dl. FIG. 20 is a plan view of the illuminationzone 4 of FIG. 19 viewed from the normal direction.

As shown in FIGS. 19 and 20, line illumination of the illumination zone4 is intermittent broken-line like illumination. The length of one lineillumination element 4 a is a predetermined length, preferably having avalue of, for example, 5 meters or 50 meters by which an accumulateddistance can be easily known. Between two line illumination elements 4 aadjacent to each other in the longitudinal direction dl, anon-illumination zone which can serve as the indicator 9 is provided.For example, when the length of one line illumination element 4 a in thelongitudinal direction dl and the length of the non-illumination zone inthe longitudinal direction dl are both 5 meters, the sum of both lengthsis 10 meters. Therefore, by counting the number of the line illuminationelements 4 a, it is easier to sharpen the sense of distance. Forexample, the distance from the forefront to the fifth line illuminationelement 4 a is about 5×10=50 meters, or more or less.

The indicators 9 of the fourth embodiment are non-illumination zoneswhich may be formed by such control of diffracted light beams from thehologram devices 3 that the diffracted light beams are not incident onthe locations corresponding to the indicators 9. As one specific exampleof control may be adjustments to diffraction fringes of the hologramdevices 3 so that light is not diffracted in the non-illumination zones.Or a scanning range of a coherent light beam from the light source 2 maybe controlled so that the coherent light beam is not incident on apartial zone on each hologram device 3.

As described above, in the fourth embodiment, the indicators 9 areprovided so that the illumination zone 4 is divided along thelongitudinal direction dl per predetermined distance. Therefore, bycounting the number of divided line illumination elements 4 a, it iseasier to recognize the distance of the illumination zone 4 in thelongitudinal direction dl.

Fifth Embodiment

A fifth embodiment prevents the occurrence of color shift at a locationin the vicinity of a light emitting component.

FIG. 21 is a figure schematically showing the optical configuration ofdiffraction optical devices 3 and their surroundings according to thefifth embodiment. An illumination apparatus 1 of FIG. 21 has a dichroicmirror 10 in addition to a plurality of hologram devices 3 on whichcoherent light beams in wavelength ranges different from one another areincident. A plurality of coherent light beams diffracted by theplurality of hologram devices 3 are incident on the dichroic mirror 10.The dichroic mirror 10 is a mirror that passes light in a specificwavelength range therethrough whereas reflects light in the otherwavelength ranges. In other words, the dichroic mirror 10 is a synthesisoptical system that combines coherent light beams diffracted in aplurality of diffraction zones, respectively, such as the plurality ofhologram devices 3.

The dichroic mirror 10 in the example of FIG. 21 reflects coherent lightbeams diffracted by hologram devices 3 for red and blue, respectively,whereas passes therethrough a coherent light beam diffracted by ahologram device 3 for green. The dichroic mirror 10 combines the threekinds of diffracted light beams and emits the combined light beam. Alight beam combined by the dichroic mirror 10 is, for example, a whitelight beam. An output light beam of the dichroic mirror 10 becomes anillumination light beam for illuminating the illumination zone 4.

As described above, by providing the dichroic mirror 10, a combinedlight beam can be generated before reaching the illumination zone 4.Therefore, color shift does not occur at a location in the vicinity of alight emitting component in such a case of superposing a plurality ofcoherent light beams on the illumination zone 4.

FIG. 22 is a figure showing one modification example of another methodof preventing the occurrence of color shift at a location in thevicinity of a light emitting component, and shows the configuration of adiffraction plane of a hologram device 3. While the illuminationapparatus 1 of FIG. is provided with a plurality of hologram devices 3corresponding to a plurality of coherent light beams, an illuminationapparatus 1 using the hologram device 3 of FIG. 22 may be provided withonly one hologram device 3.

On a diffraction plane of the hologram device 3 of FIG. 22, a pluralityof element hologram devices 3 c for diffracting, respectively, aplurality of coherent light beams in wavelength ranges different fromone another are provided in a mixed manner. The plurality of elementhologram devices 3 c are a plurality of element diffraction zones fordiffracting a plurality of coherent light beams, respectively. On thediffraction plane, the plurality of element diffraction zones arearranged in a mixed manner. In more specifically, as shown in FIG. 22,element hologram devices 3 c of the same color are provided so as not tobe next to each other in at least one of vertical and lateraldirections. Moreover, element hologram devices 3 c of each color areuniformly dispersed in the diffraction plane. Accordingly, coherentlight beams diffracted on the entire diffraction plane are incident onthe illumination zone 4 in such a state of being sufficiently mixed oneanother, so that color shift does not occur at a location in thevicinity of a light emitting unit.

As described above, in the fifth embodiment, a process of synthesis ormixing is performed before coherent light beams in a plurality ofwavelength ranges diffracted by the hologram devices 3 are incident onthe illumination zone 4, so that color shift at a location in thevicinity of the light emitting component can be reduced.

Sixth Embodiment

A sixth embodiment varies the width of a line-like illumination zone 4in the lateral direction dw.

An illumination apparatus 1 according to the sixth embodiment has thesame configuration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment. Theillumination apparatus 1 according to the sixth embodiment illuminates aline-like illumination zone 4, in the same manner as the firstembodiment. Each hologram device 3 according to the sixth embodimenthas, as shown in FIG. 23, a plurality of element hologram devices 3 carranged in the lateral direction dw of the illumination zone 4. Or, asshown in FIG. 7, a plurality of hologram devices 3 may be arranged inthe lateral direction dw of the illumination zone 4. Hereinbelow, anexample will be explained in which a plurality of hologram devices 3 areplaced vertically in the same manner as in FIG. 1 and each hologramdevice 3 has a plurality of element hologram devices 3 c arranged in thelateral direction dw of the illumination zone 4. FIG. 23 will beexplained on condition that FIG. 23 shows the configuration of one ofthe plurality of vertically-placed hologram devices 3 or a singlehologram device 3 in the illumination apparatus 1.

Each element hologram device 3 c of FIG. 23 illuminates onecorresponding partial zone 4 b extending in the longitudinal directiondl of the illumination zone 4. As shown, when there are four elementhologram devices 3 c, there are also four partial zones 4 b thatconstitute the illumination zone 4. The length of the partial zones 4 bin the longitudinal direction dl is the same as the length of theillumination zone 4 in the longitudinal direction dl whereas the lengthof each partial zone 4 b in the lateral direction dw is shorter than thelength of the illumination zone 4 in the lateral direction dw.

The light source 2 shown in FIG. 1 can switch as to whether to emitcoherent light beams to the four element hologram devices 3 c of FIG.23, separately. Such switching may be performed, for example, byproviding an optical scanning device 8 such as shown in FIG. 13 betweenthe light source 2 and the hologram device 3, and by switching thescanning range of the optical scanning device 8 to make a coherent lightbeam from the light source 2 incident on a desired element hologramdevice 3 c.

Accordingly, diffracted light beams from the element hologram devices 3c can be switched separately as to whether each light beam is guided tothe corresponding partial zone 4 b, so that the width of theillumination zone 4 in the lateral direction dw can be varied. Moreover,not only simply switching the width of the illumination zone 4 in thelateral direction dw, the plurality of partial zones 4 b divided in thelateral direction dw can be illuminated as shown in FIG. 24.

By varying the width of such a line-like illumination zone 4, forexample, it is possible to draw driver's attention on road conditionsand surrounding environment. In more specifically, when there is atraffic jam, an accident, suspension of traffic, etc. in a vehicletravel direction, the width of the illumination zone 4 can be varied todraw driver's attention in advance. Moreover, in accordance with thevehicle size, the width of the illumination zone 4 may be varied. Or inaccordance with the preference of a user, such as a driver, the width ofthe illumination zone 4 may be varied. Furthermore, in accordance withthe brightness of surroundings, the width of the illumination zone 4 maybe varied. Practically, if the surroundings are dark, the illuminationzone 4 can be visually perceived even if the width of the illuminationzone 4 is narrow, while, as the surroundings become brighter, byincreasing the width of the illumination zone 4, the illumination zone 4can be visually perceived much more.

As described above, in the sixth embodiment, since the width of theline-like illumination zone 4 in the lateral direction dw can be varied,the illumination zone 4 can be used for the purpose of drawing one'sattention or the visual perception of the illumination zone 4 can beimproved.

Seventh Embodiment

A seventh embodiment varies the length of or illumination position on aline-like illumination zone 4 in the longitudinal direction dl.

An illumination apparatus 1 according to the seventh embodiment has thesame configuration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment. Theillumination apparatus 1 according to the seventh embodiment illuminatesa line-like illumination zone 4, in the same manner as the firstembodiment. Each hologram device 3 according to the sixth embodimenthas, as shown in FIG. 24, a plurality of element hologram devices 3 carranged in the lateral direction dw of the illumination zone 4. Or, asshown in FIG. 7, a plurality of hologram devices 3 may be arranged inthe lateral direction dw of the illumination zone 4. Hereinbelow, anexample will be explained in which a plurality of hologram devices 3 areplaced vertically in the same manner as in FIG. 1 and each hologramdevice 3 has a plurality of element hologram devices 3 c arranged in thelateral direction dw of the illumination zone 4. FIG. 24 will beexplained on condition that FIG. 24 shows the configuration of one ofthe plurality of vertically-placed hologram devices 3 or a singlehologram device 3 in the illumination apparatus 1.

In the example of FIG. 24, two element hologram devices 3 c are alignedin the lateral direction dw of the illumination zone 4. These elementhologram devices 3 c are different in diffusion angle, so that adiffracted light beam of one of the element hologram devices 3 cilluminates a partial zone 4 b in the illumination zone 4, closer to theelement hologram devices 3 c, whereas a diffracted light beam of theother element hologram device 3 c illuminates a partial zone 4 b in theillumination zone 4, far from the element hologram devices 3 c.

The light source 2 can switch as to whether to emit coherent light beamsto the two element hologram devices 3 c, separately. Such switching maybe performed, as described in the sixth embodiment, for example, byproviding an optical scanning device 8 such as shown in FIG. 13. Bymaking coherent light beams incident on both of the two element hologramdevices 3 c, the length of the illumination zone 4 in the longitudinaldirection dl becomes maximum. Moreover, by making a coherent light beamincident only on either one of the element hologram devices 3 c,depending on which element hologram device 3 c a coherent light beam ismade incident on, the illumination position on the illumination zone 4in the longitudinal direction dl can be varied.

Although FIG. 24 shows an example of the hologram device 3 having twoelement hologram devices 3 c, by providing a large number of elementhologram devices 3 c, the length of the illumination zone 4 in thelongitudinal direction dl and the illumination position on theillumination zone 4 in the longitudinal direction dl can be changedfinely.

FIG. 25 is a figure explaining one modification example of FIG. 24. Byvarying the incidence angle of a coherent light beam to the hologramdevice 3, the diffraction angle on the hologram device 3 can be varied.FIG. 25 shows an example in which, when a coherent light beam isincident on the hologram device at an incidence angle a, theillumination range in the illumination zone 4 by the diffracted lightbeam of the hologram device 3 is a partial zone 4 c closer to thehologram device 3, whereas, at an incidence angle b, the illuminationrange in the illumination zone 4 is a partial zone 4 d far from thehologram device 3. Therefore, by varying the incidence angle of thecoherent light beam to the hologram device 3, the illumination positionon the illumination zone 4 in the longitudinal direction dl can bechanged. Moreover, by making a plurality of coherent light beamssimultaneously incident on the hologram device 3 from incidence angledirections different from one another, both of the partial zones 4 c and4 d can be illuminated, and accordingly, the length of the illuminationzone 4 in the longitudinal direction dl can be varied.

Although an example of varying the incidence angle to the hologramdevice 3 is shown, the optical axis direction of the illuminationapparatus 1 itself may be changed. FIGS. 26A and 26B are figuresschematically showing an example of changing an outgoing optical-axisdirection of an illumination apparatus 1 having a light source 2 and ahologram device 3. By making the outgoing optical-axis direction of theillumination apparatus 1 closer to a two-dimensional plane direction ofthe illumination zone 4, the length of the illumination zone 4 in thelongitudinal direction dl can be made longer, whereas, by tiltingfurther the outgoing optical-axis direction of the illuminationapparatus 1 obliquely downward from the two-dimensional plane directionof the illumination zone 4, the length of the illumination zone 4 in thelongitudinal direction dl can be made shorter.

As described above, in the seventh embodiment, since at least one of thelength of and the illumination position on the illumination zone 4 inthe longitudinal direction dl is changed, for example, when theillumination apparatus 1 of the present embodiment is applied to avehicle headlight, it can be performed by switching to illuminate at agreat distance such as by high-beam illumination, a short distance only,and an intermediate position between the great and short distances.

Eighth Embodiment

An eighth embodiment changes the color of a line-like illumination zone4.

An illumination apparatus 1 of the eighth embodiment has the sameconfiguration as that of FIG. 1 or FIG. 7, common with the firstembodiment, except for an illumination form of the illumination zone 4different from the illumination form of the first embodiment. Theillumination apparatus 1 according to the eighth embodiment illuminatesa line-like illumination zone 4, in the same manner as the firstembodiment.

Coherent light beams emitted from a plurality of light sources 2 aredifferent in wavelength range from one another. On each of the pluralityof hologram devices 3, a coherent light beam in the correspondingwavelength range is incident. A plurality of coherent light beamsdiffracted by the plurality of hologram devices 3 each illuminate theentire zone of the illumination zone 4. Accordingly, the illuminationzone 4 is visually perceived as having a color of coherent light beamsin a plurality of wavelength ranges mixed one another. For example, whenthe plurality of light sources 2 emit RGB three-color coherent lightbeams, the illumination zone 4 is visually perceived as having a whitecolor that is a mixture of the three colors.

The plurality of coherent light beams emitted from the plurality oflight sources 2 may have any wavelength ranges, so that the illuminationzone 4 is visually perceived as having a color depending on thewavelength ranges of the plurality of coherent light beams emitted fromthe plurality of light sources 2.

The plurality of coherent light beams to be emitted from the pluralityof light sources 2 may be switched separately as to whether to emit eachcoherent light beam. Accordingly, while using the same light sources 2,the color of the illumination zone 4 can be changed in accordance withtime. Moreover, as shown in FIG. 13, by providing an optical scanningdevice 8 that scans a plurality of coherent light beams emitted from aplurality of light sources 2 to adjust the illumination position orincidence angle to a plurality of hologram devices 3, the color can bechanged for one partial zone or for each of a plurality of partial zonesthat divide the illumination zone 4.

The present embodiment may be combined with the above-described fifthembodiment. In other words, it may be performed to control whether, on aplurality of hologram devices 3, to make corresponding coherent lightbeams incident, and a plurality of coherent light beams diffracted bythe plurality of hologram devices 3 may be combined before reaching theillumination zone 4.

As described above, in the eighth embodiment, since a plurality ofcoherent light beams in different wavelength ranges are made incident onthe corresponding hologram devices 3, the illumination zone 4 can beilluminated with a color that is a mixture of the plurality of coherentlight beams. Moreover, by arbitrarily switching the kinds of coherentlight beams to be combined, the color of the entire zone or a partialzone of the illumination zone 4 can be changed.

Ninth Embodiment

A ninth embodiment changes the illumination form of the illuminationzone 4 based on a sensor detection result, and in more specifically,switches flashing, the number of lines, width, etc. of a line-likeillumination zone 4.

FIG. 27 is a perspective view schematically showing the configuration ofan illumination apparatus 1 according to the ninth embodiment of thepresent discloser.

The illumination apparatus 1 of FIG. 27 has the same configuration asthat shown in FIG. 1, added with a sensor 11 and a light sourcecontroller 12. The sensor 11 of FIG. 27 is a detector to acquireenvironmental information on the surroundings of the illuminationapparatus 1. It does not matter about the practical type of the sensor11. For example, when the illumination apparatus 1 is used as a part ofa vehicle headlight, the sensor 11 may include an imaging unit forimaging in a vehicle travel direction, and a radar such as amillimeter-wave radar and a laser radar.

The sensor 11 may have a function of detecting whether there is anobject such as an obstacle in a vehicle travel direction. In this case,when the obstacle is found by the sensor 11 in the vehicle traveldirection, the illumination apparatus 1 can change the illumination formof the illumination zone 4 to draw driver's attention. The change in theillumination form may be performed by flashing the illumination zone 4,switching the color of the illumination zone 4 to an illumination colorthat can easily draw driver's attention such as red, or changing thenumber of lines in line illumination, which constitute the illuminationzone 4, or the illumination width.

Changing the illumination form, such as flashing, color, number of linesand width of the line-like illumination zone 4 may be performed byswitching the number of coherent light beams emitted from the lightsource 2, the incidence position or the incidence direction of thecoherent light beams from the source 2 to the hologram devices 3 fromthe light source 2. For example, illumination of the illumination zone 4may be turned on and off by the same method as that of theabove-described fourth embodiment. Or the illumination zone 4 may beilluminated with white by the same method as that of the above-describedfifth embodiment. Or the width or the number of lines of lineillumination of the illumination zone 4 may be switched by the samemethod as that of the above-described sixth embodiment. Or the color ofthe illumination zone 4 may be switched by the same method as that ofthe above-described eighth embodiment.

Moreover, the sensor 11 may have a function of detecting whether avehicle can pass through a narrow part of a road in the vehicle traveldirection, where the road width becomes narrow. In this case, inaccordance with the result of detection by the sensor 11 whether thevehicle can pass through the narrow part, the illumination form of theillumination zone 4 may be changed. Especially, when it is not possibleto pass through the narrow part, it leads to an accident if no measureis taken, so that it is desirable to illuminate the illumination zone 4in an illumination form that draws driver's attention.

Furthermore, the sensor 11 may have a function of detecting that avehicle tire goes off to the shoulder of a road from a lane area. Inthis case, when the sensor 11 detects that the vehicle tire goes off tothe shoulder of the road, the illumination form of the illumination zone4 may be changed so as to draw driver's attention.

Moreover, the sensor 11 may have a function of detecting thetemperature, humidity, brightness, etc. of the surroundings of theillumination apparatus 1. In this case, for example, when the sensor 11detects that the surroundings of the illumination apparatus 1 becomesbrighter, the illumination apparatus 1 may change the illumination formof the illumination zone 4 to raise the illumination intensity of theillumination zone 4, so that the illumination zone 4 can be visuallyperceived even though the surroundings becomes brighter. Moreover, theillumination apparatus 1 may change the illumination form of theillumination zone 4 depending on the temperature or humidity of thesurroundings.

Furthermore, the sensor 11 may have a function of detecting speed oracceleration of a vehicle equipped with the illumination apparatus 1. Inthis case, when the sensor 11 detects at least one of the vehicle'sspeed and acceleration, the illumination apparatus 1 may change theillumination form of the illumination zone 4 in accordance with thevehicle's speed or acceleration. In that case, when the sensor 11detects that the vehicle speed has reached a legal speed limit, theillumination zone 4 may be changed to an illumination form to drawdriver's attention to urge a driver to lower the speed. As describedabove, the sensor 11 may have a function of detecting a plurality ofkinds of information.

The light source controller 12 controls the timing of emitting aplurality of coherent light beams from the light sources 2 per coherentlight beam, based on a detection result of the sensor 11. In this way,the plurality of coherent light beams are controlled separately to beincident on the corresponding hologram devices 3.

As described above, in the ninth embodiment, since the illumination formof the illumination zone 4 can be changed based on the detection resultof the sensor 11, it is possible to draw the attention of a humanpresent in the surroundings of the illumination zone 4 or inform thehuman of some information. Changing the illumination form may beperformed by switching the blinking, color, number of lines, width, etc.of the line-like illumination zone 4, in accordance with the detectedcontent of the sensor 11.

Tenth Embodiment

A tenth embodiment changes the illumination form of the illuminationzone 4 based on a detection result of a sensor 11, and, in morespecifically, switches the length of a line-like illumination zone 4.

An illumination apparatus 1 of the tenth embodiment is configured in thesame manner as in FIG. 27, different from the ninth embodiment in theillumination form of the illumination zone 4.

A sensor 11 applicable to the tenth embodiment may have the samedetection functions as those of the various types of sensors 11explained in the ninth embodiment or may have other detection functions.

An illumination apparatus 1 of the tenth embodiment changes theillumination form of a line-like illumination zone 4, includingswitching the length of the illumination zone 4, based on a detectionresult of the sensor 11. In more specifically, in the tenth embodiment,based on the detection result of the sensor 11, the length of theline-like illumination zone 4 in the longitudinal direction dl isswitched. Moreover, not only the switching of the length of theillumination zone 4, but also the blinking, color, number of lines,width, etc. of the line-like illumination zone 4 may be switched.

When switching the length of the line-like illumination zone 4, the samemethod as that of the above-described seventh embodiment can be applied.In other words, among a plurality of element hologram devices 3 c in ahologram device 3, the element hologram device 3 c on which a coherentlight beam from a light source 2 is to be incident may be switched tovary the length of the line-like illumination zone 4 in the longitudinaldirection dl. Or the incidence angle at which the coherent light beamfrom the light source 2 is incident on the hologram device 3 may beswitched to vary the length of the line-like illumination zone 4 in thelongitudinal direction dl. Or the optical axis itself of theillumination apparatus 1 may be switched to vary the length of theline-like illumination zone 4 in the longitudinal direction dl.

As a specific example of the tenth embodiment, it can be considered thatthe length of the illumination zone 4 is adjusted in accordance with thebraking distance of a vehicle to stop from a point at which brakes areapplied. Accordingly, attention can be drawn to a driver. In this case,it is required for the sensor 11 to have a function of detecting thevehicle speed and a function of detecting that the driver operates abrake pedal.

In addition to above, the sensor 11 may detect an obstacle present in avehicle travel direction to adjust the length of the illumination zone 4in accordance with the distance to the obstacle. In this case, it isconsidered that, for example, the sensor 11 has a function of emittinginfrared rays to the obstacle to detect the distance to the obstacleusing the time from emission to reception of a reflected light of theinfrared rays.

As described above, in the tenth embodiment, since based on a detectionresult of the sensor 11 having various detecting functions, the lengthof the illumination zone 4 in the longitudinal direction dl is varied,it is possible to draw the attention of a human present in thesurroundings of the illumination apparatus 1 or inform the human of someinformation.

Eleventh Embodiment

An eleventh embodiment varies the irradiation angle of an illuminationlight beam from an illumination apparatus 1 based on a detection resultof a sensor 11.

An illumination apparatus 1 according to the eleventh embodiment isconfigured in the same manner as in FIG. 27, different from the ninthand tenth embodiments in the illumination form of the illumination zone4.

A sensor 11 applicable to the eleventh embodiment may have the samedetection functions as those of the various types of sensors 11explained in the ninth and tenth embodiments or may have other detectionfunctions.

An illumination apparatus 1 according to the eleventh embodiment changesthe illumination form of the illumination zone 4, including switchingthe illumination angle to the illumination zone 4, based on a detectionresult of the sensor 11. Switching the illumination angle to theillumination zone 4 may be performed by the same method as that of theabove-described seventh embodiment. For example, the illumination angleof a coherent light beam to be incident on a hologram device 3 from alight source 2 may be varied to vary the diffraction angle of thehologram device 3, and, as a result, vary the illumination angle to theillumination zone 4. In order to vary the illumination angle of thecoherent light beam to be incident on the hologram device 3 from thelight source 2, for example, as shown in FIG. 13, an optical scanningdevice 8 may be provided between the light source 2 and the hologramdevices 3 to switch the travel direction of the coherent light beam fromthe light source 2.

Or, the outgoing optical-axis direction of the illumination apparatus 1may be changed to vary the illumination angle to the illumination zone4.

As a specific example of the sensor 11, a sensor 11 having a function ofdetecting a slope present in a vehicle travel direction is considered.Specifically, it may be a vehicle height sensor attached to a vehicle oran angle of the vehicle to a road surface may be calculated by anacceleration sensor built in an ECU (Engine Control Unit). The slope tobe detected by the sensor 11 may either be a downward slope or an upwardslope. The slope detection can be performed relatively easily using aGPS sensor. Or a slope position may be detected by mapping of map datawith preregistered slope information and a vehicle position.

When an upward slope is present in a vehicle travel direction, it isdesirable to set an illumination direction at obliquely upward inaccordance with an inclination angle of the upward slope. Accordingly,it is possible to illuminate far beyond the upward slope, so that adriver can have a wider field of vision to drive more easily. Moreover,when a downward slope is present in the vehicle travel direction, it isdesirable to set the illumination direction at obliquely downward inaccordance with the inclination angle of the downward slope.Accordingly, it is possible to illuminate far beyond the downward slope,so that it is easier to drive in the same manner.

As described above, in the eleventh embodiment, since the irradiationangle of the illumination light beam is varied based the detectionresult of the sensor 11, when a slope is present in the vehicle traveldirection, it is possible to illuminate far beyond the slope.

Twelfth Embodiment

A twelfth embodiment controls a vehicle together with changing theillumination form of the illumination zone 4 based on a detection resultof the sensor 11. In more specifically, at the same time as the changingof the illumination form or when a predetermined time elapses after thechanging of the illumination form in the same manner as the illuminationapparatus 1 of any one of the ninth to eleventh embodiments, a vehicleequipped with the illumination apparatus 1 is controlled.

FIG. 28 shows the illumination apparatus of FIG. 27, added with avehicle controller 13. As the vehicle controller 13, ECU (Engine ControlUnit) and the like are listed as examples. For example, although thesensor 11 detects an obstacle in a vehicle travel direction and theillumination apparatus 1 changes the illumination form of theillumination zone 4 to draw the driver's attention, even when a driverdoes not notice illumination for drawing attention, the vehiclecontroller 13 can control a vehicle to take action to avoid theobstacle.

As an example of practical control method, the light source controller(detector) 12 acquires environmental information through the sensor 11and, based on the acquired environmental information, the vehiclecontroller 13 changes the illumination form.

In more specifically, after changing the illumination form, when thereis no change in the vehicle after the elapse of a predetermined time,the vehicle controller 13 may control the vehicle. As specific examplesof vehicle control, it may be performed to restrict the engine output,operate the brakes or operate the transmission to decelerate thevehicle. Or the staring wheel may be operated to change the vehicledirection.

Whether there is change in the vehicle is determined by the vehiclecontroller 13 based on detection information of the sensor 11 acquiredby the light source controller (detector) 12.

After controlling the vehicle in conjunction with the change inillumination form based on the detection information of the sensor 11,if vehicle control is not needed, it may be performed to return theillumination form to the original form and the vehicle to the statebefore being controlled.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

The invention claimed is:
 1. An illumination apparatus that illuminatesan illumination zone having a first direction and a second directioncrossing the first direction comprising: a light source to emit aplurality of coherent light beams having different wavelengths ranges;and a diffraction optical device to diffract the plurality of coherentlight beams incident from the light source so that a width of theillumination zone in the second direction gradually becomes wider alongthe first direction of the illumination zone from a nearer side to thediffraction optical device, wherein the diffraction optical devicecomprises: a plurality of diffraction zones provided corresponding tothe plurality of coherent light beams, respectively, the diffractionzones diffracting the corresponding coherent light beams to illuminatethe illumination zone; and a synthesis optical system to combine thecoherent light beams diffracted by the plurality of diffraction zones,respectively, wherein the illumination zone is illuminated with acoherent light beam combined by the synthesis optical system.
 2. Theillumination apparatus of claim 1, wherein a diffusion angle of thecoherent light beams diffracted by the diffraction optical device in thesecond direction of the illumination zone is constant in an entire zoneof the illumination zone in the first direction.
 3. The illuminationapparatus of claim 1, wherein the diffraction optical device diffractsthe plurality of coherent light beams incident from the light source sothat indicators are displayed in at least part of the illumination zonein the first direction.
 4. The illumination apparatus of claim 3,wherein the indicators are displayed at a predetermined interval in thefirst direction of the illumination zone, an illumination form of theindicators being different from an illumination form of the illuminationzone.
 5. The illumination apparatus of claim 3, wherein the indicatorsare displayed at an end of the illumination zone in the first direction,an illumination form of the indicators being different from anillumination form of the illumination zone.
 6. The illuminationapparatus of claim 3, wherein the indicators are arranged so as todivide the illumination zone per predetermined distance along the firstdirection.
 7. The illumination apparatus of claim 1, wherein the lightsource emits the plurality of coherent light beams in wavelength rangesdifferent from one another, wherein the diffraction optical devicecomprises a diffraction plane, the plurality of coherent light beamsbeing incident on the diffraction plane, a plurality of elementdiffraction zones to diffract the plurality of coherent light beams,respectively, are arranged on the diffraction plane in a mixed manner,and each of the plurality of element diffraction zones illuminates theillumination zone.
 8. An illumination apparatus that illuminates anillumination zone having a first direction and a second directioncrossing the first direction comprising: a light source to emit acoherent light beam; and a diffraction optical device to diffract thecoherent light beam incident from the light source, wherein thediffraction optical device comprises a plurality of diffraction zones,the plurality of diffraction zones illuminating partial zones that arearranged in the second direction in the illumination zone and differentfrom one another, and wherein the light source and the diffractionoptical device change an illumination form of the illumination zone, theillumination form including at least one of a width of the illuminationzone in the second direction, a number to divide the illumination zonein the second direction, and an illumination length of the illuminationzone in the first direction, by switching whether the coherent lightbeam is incident on the plurality of diffraction zones.
 9. Theillumination apparatus of claim 8, wherein an illumination position onthe illumination zone in the first direction is changed by switching anincidence angle of the coherent light beam from the light source to thediffraction optical device.
 10. The illumination apparatus of claim 8,wherein an illumination position on the illumination zone in the firstdirection is changed by switching an outgoing optical axis of theillumination apparatus.
 11. The illumination apparatus of claim 8,wherein an illumination color of the illumination zone is changed byswitching whether a plurality of coherent light beams having differentwavelength ranges are incident on the plurality of diffraction zones.12. An illumination apparatus that illuminates an illumination zonehaving a first direction and a second direction crossing the firstdirection comprising: a light source to emit a coherent light beam; adiffraction optical device to diffract the coherent light beam incidentfrom the light source; and a detector to acquire environmentalinformation on surroundings of the illumination apparatus, wherein thelight source and the diffraction optical device change an illuminationform of the illumination zone based on the environmental informationacquired by the detector, the illumination zone is a zone to illuminatepart of a road along a travel direction of a vehicle running on theroad, the detector detects an obstacle in front in a running directionof the vehicle, and the light source and the diffraction optical devicechange an illumination form of the illumination zone when the detectordetects the obstacle.
 13. An illumination apparatus that illuminates anillumination zone having a first direction and a second directioncrossing the first direction comprising: a light source to emit acoherent light beam; a diffraction optical device to diffract thecoherent light beam incident from the light source; and a detector toacquire environmental information on surroundings of the illuminationapparatus, wherein the light source and the diffraction optical devicechange an illumination form of the illumination zone based on theenvironmental information acquired by the detector, the illuminationzone is a zone to illuminate part of a road along a travel direction ofa vehicle running on the road, the detector detects at least one ofspeed and acceleration of the vehicle, and the light source and thediffraction optical device change an illumination target of theillumination zone based on the at least one of the speed andacceleration of the vehicle detected by the detector.